Re: Why they call the epicenter of an earthquake 'ground zero'

Good question.  The term "Ground Zero" comes from the military world where 
it refers to the exact location where a bomb hits.  Around that spot are 
drawn concentric circles labeled G+5, G+10, G+50... and so on showing how 
far out from the impact point the circle is.

Since it is the impact point for the bomb, it is, of course, the point of 
highest damage.  That's how the term came to be used with earthquakes - it 
is the point of highest damage.

The epicenter of an earthquake is the spot on the surface of the Earth 
directly over the source of the quake.  Since it is closest to the actual 
source (which may be kilometers deep in the Earth), the epicenter is often 
(but not always) the point of greatest damage - thus Ground Zero